PURPOSE: In this study, we examined whether additional, delayed regional FDG PET scans could increase the accuracy of the lymph node staging of NSCLC patients. MATERIALS AND METHODS: Among 87 patients who underwent open thoracotomy or mediastinoscopic biopsy under the suspicion of NSCLC, 35 (32 NSCLC and 3 infectious diseases) who had visible lymph nodes on both preoperative whole body scan and regional FDG PET scan were included. The following 3 calculations were made for each biopsy-proven, visible lymph node: maximum SUV of whole body scan (WB SUV), maximum SUV of delayed chest regional scan (Reg SUV), and the percent change of SUV between WB and regional scans (% SUV Change). ROC curve analyses were performed for WB SUVs, Reg SUVs and % SUV Changes. RESULTS: Seventy lymph nodes (29 benign, 41 malignant) were visible on both preoperative whole bodyscan and regional scan. The means of WB SUVs, Reg SUVs and % SUV Changes of the 41 malignant nodes, 3.71+/-1.08, 5.18+/-1.60, and 42.59+/-33.41%, respectively, were all significantly higher than those of the 29 benign nodes, 2.45+/-0.73, 3.00+/-0.89, and 22.71+/-20.17%, respectively. ROC curve analysis gave sensitivity and specificity values of 80.5% and 82.8% at a cutoff of 2.89 (AUC 0.839) for WB SUVs, 87.8% and 82.8% at a cutoff of 3.61 (AUC 0.891) for Reg SUVs, and 87.8% and 41.4% at a cutoff of 12.3% (AUC 0.671) for % SUV Changes. CONCLUSION: Additional, delayed regional FDG PET scans may improve the accuracy of lymph node staging of whole body FDG PET scan by providing additional criteria of Reg SUV and % SUV Change.